Town officials say they expect the developer, Daniel Bertram, the president of BRT Corp., to submit the site plan sometime late this spring.

The site plan is a professionally prepared engineered drawing of the proposed project and includes a detailed presentation of what the project will look like, with features including the type and location of light fixtures, plantings and interior roads.

The site plan will be submitted to the Planning and Zoning Commission for its review and approval.

Meanwhile, supporters of the estimated $30 million project and town officials alike both say Fred Hassan, the owner of the 14.7-acre former hospital site, was key to getting a final agreement approved.

In an email he sent Tuesday night following the signing of the agreement, Bertram said, “I give full credit to Fred. He was overwhelmed by the support from the people in town,” Bertram said.

Indeed, Hassan was so overwhelmed “he decided to absorb the effect of the selectmen’s not approving our final proposal,” Bertram said.

“In response, we could not do anything, but agree to proceed, given his commitment to give Portland the development they want,” Bertram said.

In comments Thursday morning, First Selectwoman Susan S. Bransfield agreed Hassan was key to a successful conclusion of the debate over the tax abatement.

In turn, Bransfield said Hassan was inspired to come forward because of “the outpouring of support for the project on the part of so many Portland residents.

“To get to this point has involved a three-legged stool with the owner, the developer and the grassroots support of so many residents,” Bransfield said. “Fred’s been working with the town for a long time to redevelop the site.”

Hassan first approached her about redeveloping the property around 2005-06, Bransfield said.

Hassan, who was the accountant for Elmcrest when it was a hospital, bought the property in a partnership with two doctors. Once the hospital closed, the three partners began planning for a way to redevelopment the site, a portion of which is planted with specimen trees and which also contains a number of architecturally interesting and historic building.

The two doctors died, but Hassan has continued on.

During a tour of the property last summer, Hassan said he was committed to redeveloping the property in such a way to honor the vision of his deceased partners.

In response to the announcement that the town had reached agreement with Bertram, state Rep. Christie Carpino emailed a message: “Good news. We need to move forward as a town.”

For his part, Elwin Guild, the chairman of the Economic Development Commission and a consistent supporter of the project, said the agreement “means Bertram is now on second base.